Synchronous Optical NETworking (SONET), is a method for communicating digital information using lasers or light-emitting diodes (LEDs) over optical fiber. There are multiple, very closely related standards that describe synchronous optical networking; Synchronous Digital Hierarchy (SDH) standard developed by the International Telecommunication Union (ITU), documented in standard G.707 and its extension G.708; and SONET as defined by GR-253-CORE. Optical networks typically comprise an array of different network elements, such as SONET network elements (NEs). Example SONET NEs include path terminating elements or terminal multiplexer, regenerators, add/drop multiplexers, cross-connects, and digital loop carriers. These network elements can be deployed in a variety of system architectures, such as point-to-point architectures, point-to-multipoint architectures, hub network architectures, and ring architectures.
SONET equipment is often managed with the Transaction Language 1 (TL1) protocol. TL1 is a telecom language for managing and reconfiguring SONET network elements. TL1 (or whatever command language a SONET Network Element utilizes) can be carried by other management protocols, including Simple Network Management Protcol (SNMP), Common Object Request Broker Architecture (CORBA) and eXtensible Markup Language (XML). One possible application for TL1 is for a management system (or NE) to package its trap/notification data in TL1 format and forward it to a network management component. An network management component may also provide a TL1-based facility for sending commands to the lower layers.
Most SONET NEs have a limited number of management interfaces defined. These may include electrical interfaces operative to send SONET TL1 commands from a local management network physically housed in the Central Office where the SONET NE is located. The electrical interface can be used for local management of the NE and, possible, remote management of other SONET NEs. In addition, a craft interface provides access to a SONET NE through a dumb terminal or terminal emulation program running on a laptop. This interface can also be hooked-up to a console server, allowing for remote out-of-band management and logging. In addition, SONET/SDH NEs may include dedicated Data Communication Channels (DCCs) for management traffic. Typically, one connection can reach all network elements within a given architecture; that is, separate links are not required for each network element.
The main functions of SONET Network Management typically include network and network element provisioning, software upgrades and performance management. In order to allocate bandwidth throughout a SONET Network, each SONET NE is configured. Although this can be done locally, through a craft interface, it is normally done through a Network Management System (siting at a higher layer) that in turn operates through the SONET/SDH Network Management Network. SONET NE Software Upgrade is in modern NEs done mostly through the SONET/SDH Management/network. SONET NEs have a very large set of standards for Performance Management. The PM criteria allow for monitoring not only the health of individual NEs, but for the isolation and identification of most network defects or outages. Higher-layer Network monitoring and management software allows for the proper filtering and troubleshooting of network-wide PM so that defects and outages can be quickly identified.
Additionally, SONET/SDH networks typically provide protection from failure by using topologies that dedicate half of the total bandwidth for protection. One type of SONET protection is bi-directional line switched ring (BLSR). The BLSR may be two-fiber or four-fiber. BLSR provides rapid restoration times with control logic. In a BLSR, traffic can be added and dropped at any node along a given ring. At the drop site, new traffic can be added to the previously used time slot and transported further around the ring. This re-use of bandwidth in a BLSR increases the capacity for the entire ring and provides many advantages over a unidirectional path switched ring (UPSR). If a fiber is cut in the BLSR, multiplexers have the speed to send the services affected via and alternate acceptable path through the ring without interruption.
When a BLSR is provisioned, each node in the BLSR is configured with knowledge as to what other nodes are in the same ring. Traditionally, BLSR software receives a list of IP addresses that a local BLSR node discovered. In order to determine if there are any other BLSR nodes in the list, the local node sends a message (e.g., UDP socket message) to each node and queries it. Upon receiving the message, a BLSR node replies by sending a respond message back with a valid BLSR node ID. A non-BLSR node will also will also send a respond message back but with a non-ring-node-id. The software generates a BLSR ring map after it receives all of the replies.
When new software for a SONET/SDH network element is delivered to the customer, a customer's test engineers typically perform a series of acceptance tests to check if the software is acceptable-such as the operation of automatic protection switching mechanisms.